Tiny vibrating bubbles could lead to better water treatment
Fresh research into the physics of vibrating nanobubbles reveals that they do not heat up as much as previously thought.
Fresh research into the physics of vibrating nanobubbles reveals that they do not heat up as much as previously thought.
Vibrating nanobubbles have surprising uses as ultrasound contrast agents in cancer diagnosis. They can also be forced to collapse - destroying nearby microscopic contaminants - for waste-water treatment and surface cleaning of delicate microfluidic devices.
The stiffness of a nanobubble as it vibrates is strongly related to their internal temperature, and being able to understand this relationship leads to better predictions of their size in experiments and their design in these applications.
Using ARCHER2, the UK’s national leading supercomputer hosted at the University of Edinburgh, the research found two distinct nanoscale effects that influence bubbles with diameters less than one thousandth of a millimetre across.
The high density of the gas inside the bubbles leads to molecules bouncing off each other more frequently, resulting in an increased bubble stiffness, even at constant temperatures.
Another effect from the nanoscale dimensions of the bubble was the emergence of an insulating layer around the bubble, which reduced the ability for the bubble to dissipate the internal heat, which modified the way they vibrated.
The study revealed the true pressure and temperature distributions inside nanobubbles, using high-detail molecular dynamics simulations, and found a better model to describe their dynamics.
Study lead, Dr Duncan Dockar, RAEng Research Fellow, School of Engineering, University of Edinburgh, said:
“The results of these findings will allow us to employ nanobubbles for better efficiencies in water-treatment processes and precise cleaning of microelectronic devices.
“This work also highlights the roles of bubbles in future nanotechnologies, which have been seeing a lot interest in recent years. Our upcoming research focuses on the unusual nanoscale effects that influence these bubbles, which are not common in everyday engineering.”
The research, published in Nano Letters, was funded by EPSRC.
JOURNAL
Nano Letters
METHOD OF RESEARCH
Experimental study
ARTICLE TITLE
Thermal Oscillations of Nanobubbles
A new design improves water decontamination via plasma jet
IMAGE:
THE RESEARCHERS FRANCISCO J. ROMERO, JUAN AMARO AND MARIA C GARCÍA
view moreCREDIT: UNIVERSITY OF CORDOBA
Two UCO research groups design a plasma (an ionized gas) reactor maintained by microwaves that makes it possible to decontaminate waters with high concentrations of dye
Plasma is an ionized gas - that is, a gas containing electrons, ions, atoms, molecules, radicals, and photons. It is often called the fourth state of matter and, surprisingly, it permeates everything. Plasmas, which are artificially generated by transmitting energy to a gas, are found in the fluorescent tubes that light kitchens, but they have also allowed mobiles to become smaller and smaller.
Plasma has been a veritable revolution in the world of technology. Before, to engrave the circuits on the silicon plates used in electronic devices like mobile phones, it was necessary to use polluting chemical products. Now, the use of plasma has made it possible to do this more cleanly and precisely, it being possible to make the slits smaller and smaller, and, with them, the devices.
But plasma has other applications too, such as water treatment. The FQM-136 Physics of Plasmas and FQM-346 Organic Catalysis and Nanostructured Materials groups at the University of Cordoba collaborated on a research study whose purpose was the elimination of contaminants present in water by applying plasma to promote chemical processes.
With the aim of tackling the problem of the increasing presence of organic pollutants in waters, such as dyes and other compounds from agricultural and industrial activity in waters that destabilize ecosystems, these researchers opted for the application of plasma.
In 2017 they demonstrated, for the first time, that the argon plasmas induced by microwaves open to the air, when acting on water, generated in it reactive species containing oxygen and nitrogen (such as hydroxyl radicals, hydronous peroxide, nitrogen radicals) capable of decontaminating it. Now the researchers Juan Amaro Gahete, Francisco J. Romero Salguero and María C. García have managed to design a reactor of this type of plasma and to significantly increase the amounts of these active species generated in water, thus making possible the destruction of high concentrations of dyes (in this case, methylene blue) in just minutes.
This was achieved by altering the design of the surfatron, the metal device that mixes the energy from a microwave generator with the plasma to maintain it. "What we've done is to place a small piece of silicon in the quartz discharge tube, allowing a different plasma to be generated, one that is not filamentary and is more efficient at creating active species when interacting with water," explained Professor María C. García. The aforementioned plasma components, when interacting with water, generate oxidizing species capable of degrading organic compounds and killing microorganisms, which allows this plasma reactor to be used in applications related to water remediation.
This new configuration, therefore, expands the applicability of this type of plasmas. "The design completely changes the configuration of the electromagnetic field generated by the surfatron to create the plasma, resulting in plasma with different and more efficient properties, also eliminating the problem of filamentation (the division of the plasma column into many filaments), which destabilizes it," explained Professor García.
And then...decontamination. "Those oxidizing species generated due to the action of plasma are very reactive and make it possible to destroy the organic matter inside the water," continued Professor Francisco J. Romero. For this to happen, the plasma is not introduced into the water. Rather it is made to act remotely, so that between the water and the plasma there is a zone of air where numerous reactions occur due to collisions between the excited species and the molecules of oxygen, nitrogen and water vapor, and "reactive species that diffuse into the liquid and end up with the contaminants" are generated.
The decontaminating potential of this type of plasma, generated with this new design "has been tested to reduce high concentrations of methylene blue dye in water, with very efficient results in terms of energy, achieving the complete elimination of the dye at reduced treatment times," said researcher Juan Amaro.
Thus, with this work progress is made on one of the applications of plasma, that "fourth state of matter" created by providing a stable gas with energy and converting it into an ionized gas, with this being applicable to almost everything: manufacturing microchips, disinfecting surfaces, healing wounds, depositing anti-reflective coatings on glasses, improving seed germination, recovering waste, activating the surface of plastics to achieve better paint adhesion, and countless other applications.
Reference
Amaro-Gahete J, Romero-Salguero FJ, Garcia MC. Modified surfatron device to improve the microwave-plasma-assisted generation of RONS and methylene blue degradation in water. Chemosphere. 2024 Feb;349:140820. doi: 10.1016/j.chemosphere.2023.140820.
JOURNAL
Chemosphere
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Modified surfatron device to improve microwave-plasma-assisted generation of RONS and methylene blue degradation in water
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